The intermediolateral cell column of the thoracic spinal cord (IML) receives both noradrenergic (NE) and adrenergic (E) inputs from the brainstem. According to existing data, one of these pathways could represent a neuronal link in the baroceptor-mediated inhibition of the sympathetic outflow to the heart and blood vessels. The evidence is very indirect however and in particular the specific role of the dual catecholaminergic innervation of the IML (via NE and E fibers) is still totally unaccounted for. The aim of the present proposal is therefore to analyze in further details the physiology of the catecholaminergic inputs to the IML and to determine to which extent they are involved in the central regulation of blood pressure. Three complementary approaches are proposed. Firstly, the electrophysiological characteristics of the catecholaminergic neurons located in the lateral reticular formation will be examined with single-unit recording techniques in the rat. This nucleus contains the adrenergic neurons presumed to project the IML. The effect of blood pressure changes and antihypertensive drugs on the discharges of these neurons will be investigated. Secondly, the responses of sympathetic preganglionic neurons (SPN's) to the iontophoretic application of catecholamines will be determined in the IML of the cat. The principal aim of this series of experiments will be to determine the number and pharmacological specificity of the receptors involved in the synaptic action of catecholamines at this level. Finally, the release of catecholamines will be monitored directly in the IML of the cat using "in vivo" electrochemical detection. The main purpose of these experiments will be to determine whether the release of catecholamines in the IML is influenced by changes in peripheral blood pressure and secondarily to study how it is affected by centrally-acting antihypertensive drugs. The proposed experiments must be viewed as a first step in a larger research effort directed at understanding the physiology of central pathways involved in the control of blood pressure and the sympathetic outflow.